Igniter plug

ABSTRACT

An igniter plug for a turbine engine capable of operating at high temperatures without failure of internal pressure seals that prevent the leakage of gases from the combustion chamber of the turbine through the igniter plug that adversely affect the ignition exciter assembly. The novel internal pressure seal within the igniter plug includes a cylindrical metal sleeve having a first portion brazed to an intermediate insulator that surrounds a central electrode and a second portion of larger diameter that has its edge welded around the periphery thereof to the igniter plug shell. This arrangement allows the igniter plug shell and intermediate insulator to expand and contract in response to extreme changes in temperature without breaking the pressure seal between the shell and the insulator.

United States Patent [19 1 Meyer [11] 3,745,400 1 July 10, 1973 IGNITER PLUG [75] Inventor: Helmut P. Meyer, Sidney, N.Y.

[73] Assignee: The Bendix Corporation, Southfield,

Mich.

[22] Filed: Mar. 23, 1972 [21] Appl. No.: 237,306

[52] US. Cl. 3l3/l44, 3l3ll38 [51] Int. Cl. H0lt 13/00 [58] Field of Search 313/138, 144

[56] g References Cited UNITED STATES PATENTS 3,229,144 Ill-966 Poland ..3l3/l38 Primary Examiner-Roy Lake Assistant Examiner-Darwin R. Hostetter Attorney-Raymond .l. Eifler et al.

[57] ABSTRACT An igniterplu'g for a turbine engine capable of operating at high temperatures without failure of internal pressure seals that prevent the leakage of gases from the combustion chamber of the turbine through the igniter plug that adversely affect the ignition exciter assembly. The novel internal pressure seal within the igniter plug includes a cylindrical metal sleeve having a first portion brazed to an intermediate insulator that surrounds a central electrode and a second portion of larger diameter that has its edge welded around the periphery thereof to the igniter plug shell. This arrangement allows the igniter plug shell and intermediate insulator to expand and contract in response to extreme changes in temperature without breaking the pressure seal between the shell and the insulator.

4 Claims, 2 Drawing Figures IGNITER PLUG BACKGROUND OF THE INVENTION This invention relates to a spark discharge device for igniting combustible materials and more particularly to an improved igniter plug for igniting fuel in a turbine engine. The invention is most particularly related to a novel internal pressure seal within the igniter plug that prevents the escape of gases from the engine.

Igniter plugs generally comprise a metal shell or body that has a flange or other mounting means for mounting the igniter plug in a turbine engine, the shell constituting one electrode of the igniter plug. A central electrode passes through the shell and is supported by an insulator which surrounds the central electrode and which is fitted into an opening in the metal shell. A copper packing ring or bushing is then provided between the insulator and the shell in order to seal the opening in the body, through which the insulator extends, against escape of gases. Even though the seal is initially tight, the copper packing will, after a period of use under the pressures encountered in the engine and under the repeated action of heating and cooling and under vibration, become loose and permit the escape of gases which will allow engine pressure to leak through the igniter plug. Of the aforementioned conditions thermal expansion and contraction has been the predominant problem, as no matter what type of sealing mechanism is used, expansion and contraction of the shell and insulator would eventually cause the sealing mechanism to break free and allow gases to escape. An example of one prior art approach to this problem may be found in U.S. Pat. No. 2,937,296 entitled Spark Discharge Device, issued May 17, 1960 to J. J. Logan. In the Logan igniter plug device a metal diaphragm located between the insulator and the shell had one end brazed to the insulator and the other end brazed to the shell. In actual use it was found thatthermal expansion and contraction during use caused failure of the brazed portions-so that gases leaked from the engine. Investigations of the failures revealed the fact that during operation, thermal expansion of the metal shell made the inner diameter of the shell larger while thermal expansion of the ceramic insulator diameter was less than the expansion of the inner diameter of the shell which resulted in an increase in the radial distance between the insulator and the shell. This increase in radial distance causes stresses between the diaphragm and the shell or insulator that cause failure of one of the brazed connections.

Therefore, present day spark discharge devices do not provide an internal pressure seal between the insulator and shell that operate satisfactorily over long periods of time when subjected to frequent thermal expansion and contraction.

SUMMARY OF THE INVENTION This invention provides an igniter plug for turbine engines that has a greater capability of preventing the escape of gas from the engines than previous igniter plugs.

The invention is an improved igniter plug characterized by a pressure sealing metal diaphragm that has the inside of one end portion brazed to the insulator that surrounds the central electrode and the other end welded to the end of the igniter shell.

In one embodiment of the invention the igniter plug comprises an inner elongated electrode (30); and intermediate insulator (40) surrounding the electrode; an outer elongated metal shell (20) coaxially arranged around the electrode and the insulator; and a metal diaphragm (1) that has one portion brazed (11) to the insulator and one end welded (21) to the shell so that the rear portion of the diaphragm can compensate for radial and axial movement of the insulator and shell, thereby retaining a pressure-tight seal between the pressurized gases within the engine and atmosphere.

Accordingly, it is an object of this invention to provide an igniter plug that includes a pressure sealing metal diaphragm that can be subjected to greater radial and axial expansion and contraction than previous devices without failing.

It is another object of this invention to provide a method and apparatus for bonding a diaphragm to a ceramic insulator and a metal shell that compensates for the radial and axial expansion therebetween.

It is still another object of this invention to provide a method of constructing an igniter plug whereby a gastype seal is assured between the inside of the engine and the outside atmosphere.

The above and other objects and features of the invention will become apparent from the following detailed'description taken in conjunction with the accompanying drawings and claims which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional diagram of an igniter plug that utilizes the principles of this invention.

FIG. 2 is a cutaway view of thediaphragm that is used to accomplish the objects of this invention.

DETAIL DESCRIPTION OF THE DRAWINGS Referring now to the drawings, FIG. 1 illustrates an igniter plug wherein there is a fluid-tight seal between the central electrode30 and the outer shell 20. The term fluid-tight or pressure-tight when used herein means a seal between two members that prevents the flow of fluid, such as gas, even under pressure, between the two members.

The igniter plug comprises an elongated central electrode 30; a ceramic insulator 40; a first metal diaphragm 50; the outer metal shell 20 which forms the from which the spark discharge occurs includes a cylin-' drically shaped end portion that is of a much larger diameter than the rest of the electrode which contains therein one or more passages 31 for the passage of gas to cool the tip of the electrode 30 during operation.

Surrounding most of the central electrode 30 is a ceramic insulator 40 which electrically isolates the central electrode 30 from the outer shell electrode 20. To prevent any gases from escaping through the bore 41 of the insulator 40, a first diaphragm 50 connects (brazed) and seals in fluid-tight relationship the insulator 40 and the center electrode 30.

The first diaphragm 50 is generally comprised of a metallic material that is brazed to form a continuous 360 bond 51 between the first diaphragm 50 and a portion of the inside of the insulator 40. To assure a fluid-tight seal between the first diaphragm 50 and the central electrode 30, first diaphragm 50 is brazed to the central electrode to form a continuous 360 degree bond 52.

In accordance with standard igniter plug fabrication, a cylindrical copper wedge seal 60 is located between the outer shell 20 and intermediate insulator 40.

A second forward ceramic insulator 80 having a shoulder 81 is also positioned within the shell 20 to prevent radial and axial movement of the control electrode 30 that might result in contact between the control electrode 30 and the shell electrode 20, hence preventing electrical short circuits.

The outer shell 20 includes a mounting flange 21 for mounting the igniter plug in a turbine engine; intake and exhaust ports 24, 25, 26 for allowing the entrance and exit of engine gases into the igniter plug to cool the electrode 30; and a forward shell portion or cap 23 that is welded to the shell 20 at point 29. The front portion of the shell cap 23 includes an opening 22 that forms the discharge surface of the shell electrode 20 that with the discharge surface 32 of the control electrode 30 forms the discharge gap. When assembling the igniter plug, the last two pieces added to the assembly are the forward ceramic insulator 80 and then the shell cap 23 which when welded to the shell 20 retains the forward insulator 80.

The second diaphragm 1 is preferably a metallic material, such as a nickel iron alloy chosen for its resilient features over a wide range of temperatures to 700F), and is concentrically arranged around the intermediate insulator 40. The forward portion of the diaphragm 1 is brazed to the insulator 40 to form a continuous 360 bond 11 between the insulator 40 and the second diaphragm l. The opposite end of the diaphragm 1 is welded to the shell to form a continuous 360 bond 12 between the diaphragm i and the shell 20. It is important to note at this particular point that the second diaphragm 1 is assembled between the insulator 40 and the shell 20 in a position opposite to that of any previous type igniter plug. This approach allows a method of attachment which is different from all other igniter plugs which, in the reverse position, had both the inner and outer cylindrical surfaces of the diaphragm brazed to the insulator and the shell respectively. It was this prior approach of brazing each end that limited the capability of previous igniter plugs with respect to compensating for radial and axial expansion without failure of the bond. In the arrangement shown in FIG. 1, the weld l2 connecting the diaphragm l to the shell 20 functions as a hinge to compensate for an increase in the radial distance, together with the rear end portion 2 of diaphragm 1, between the outside of the insulator 40 and the inside of the shell 20.

FIG. 2 illustrates a cutaway view of the second diaphragm 1 that is welded to the shell 20 and brazed to the insulator 40. The diaphragm includes a cylindrical rear portion 2 connected to a cylindrical front portion 4 which is of a smaller diameter than the rear portion connected together by a conical portion 3 which has an axis of rotation B that makes an angle of 45 degrees with the axis A of the cylindrical portions. The connecting link 3 between the two cylindrical portions is preferably at an angle less than degrees so as to provide some resilience between the two cylindrical portions and is preferably between 35 and 55 degrees. It is this conical portion 3 and the larger cylindrical portion 2 that compensates for most of the axial and radial expansion of and between the insulator 40 and shell 20. This portion, by flexing, allows the shell 20 and insulator 40 to expand and contract without breaking the integrity of the pressure-tight seal therebetween. Another advantage of connecting the diaphragm l to the shell 20 by a weld is that a weld is capable of operating at higher temperatures under greater stresses and strains than a brazing bond without failure.

While a preferred embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that changes may be made to the invention as set forth in the appended claims and, in some cases, certain features of the invention may be used to advantage without corresponding use of other features. For example, in addition to the second diaphragm 1 at the end of the igniter plug, a third diaphragm may be introduced farther down the insulator. In such an instance the rear portion of the shell 20 could be made of more than one piece so that there would be an internal shoulder beneath the external mounting flange 21 for welding of the third diaphragm thereto. Further, the configuration of the diaphragm 1 may be shaped to match the configuration of the inner diameter of the shell 20 and the outer diameter of the insulator 40 where the weld and braze are made, respectively. Obviously, coaxial cylindrical tubes are the easiest shapes to work with but the invention is not limited to those shapes. Accordingly, it is intended that the illustrative and descriptive materials herein be used to illustrate the principles of the invention and not to limit the scope thereof.

Having described the invention, what is claimed is:

1. In combination with a spark plug of the type having an inner elongated electrode having a front portion and a rear portion; an intermediate elongated insulator disposed around at least a portion of the electrode, said insulator having a front portion and a rear portion; means for providing a pressure tight seal between said inner electrode and said elongated insulator; an outer elongated metal shell disposed around the electrode and electrically isolated therefrom by the insulator, said metal shell having a rear portion that has an opening therein and a front end portion arranged to provide a spark gap with the end of the front portion of said electrode, the improvement comprising:

a metal sleeve having a front end portion that includes an opening that is in mated relationship with the rear portion of said insulator, the inside of said front end portion of said sleeve annularly brazed to the outside rear portion of said insulator; and a rear end portion having a configuration that matches the opening in the rear of said metal shell, the rear end of said metal sleeve annularly welded to the rear end of said metal shell, said metal sleeve comprised of a single piece of metal that has two cylindrical portions of different diameters connected together by a third portion having an axis of revolution that makes an angle with the axis of said cylindrical portions between about 35 to 55 degrees, whereby said insulator and said shell are connected together by said sleeve.

2. The combination as recited in claim 1 wherein the opening in the front end portion of said metal sleeve is smaller than the opening in the rear end portion of said metal sleeve.

3. The combination as recited in claim 1 wherein said 5 electrode, said insulator, said shell and said metal sleeve are generally cylindrical and concentrically arranged. 

1. In combination with a spark plug of the type having an inner elongated electrode having a front portion and a rear portion; an intermediate elongated insulator disposed around at least a portion of the electrode, said insulator having a front portion and a rear portion; means for providing a pressure tight seal between said inner electrode and said elongated insulator; an outer elongated metal shell disposed around the electrode and electrically isolated therefrom by the insulator, said metal shell having a rear portion that has an opening therein and a front end portion arranged to provide a spark gap with the end of the front portion of said electrode, the improvement comprising: a metal sleeve having a front end portion that includes an opening that is in mated relationship with the rear portion of said insulator, the inside of said front end portion of said sleeve annularly brazed to the outside rear portion of said insulator; and a rear end portion having a configuration that matches the opening in the rear of said metal shell, the rear end of said metal sleeve annularly welded to the rear end of said metal shell, said metal sleeve comprised of a single piece of metal that has two cylindrical portions of different diameters connected together by a third portion having an axis of revolution that makes an angle with the axis of said cylindrical portions between about 35 to 55 degrees, whereby said insulator and said shell are connected together by said sleeve.
 2. The combination as recited in claim 1 wherein the opening in the front end portion of said metal sleeve is smaller than the opening in the rear end portion of said metal sleeve.
 3. The combination as recited in claim 1 wherein said electrode, said insulator, said shell and said metal sleeve are generally cylindrical and concentrically arranged.
 4. The combination as recited in claim 2 wherein said electrode, said insulator, said shell and said metal sleeve are generally cylindrical and concentrically arranged. 